Water injection induced crack early warning method based on area water injection well network

Abstract

The invention discloses a water injection induced crack early warning method based on an area water injection well network. The water injection induced crack early warning method comprises the following steps that reservoir ground stress characteristic parameters, rock mechanics parameters, oil reservoir development characteristic parameters and oil reservoir injection-production parameters are obtained; for the interior of the injection-production well group, an area water injection well network is adopted for deployment, and the opening critical pressure of the water injection induced crack in each injection-production connecting line direction in the well group is calculated; selecting the minimum value of the critical water injection pressure in each direction of the injection-production connecting line as early warning water injection pressure, and taking the corresponding direction as an early warning direction; calculating a single well water injection induced crack opening critical water injection intensity as an early warning water injection intensity; and single well water injection induced crack early warning is carried out. The problems that an existing water injection induced crack prediction result is inaccurate and poor in reliability are solved.

Description

Technical Field

[0001] This invention belongs to the field of oilfield development technology, specifically relating to a method for early warning of water injection-induced fractures based on an area-based water injection well network. Background Technology

[0002] During water injection development, existing technologies, from the perspective of well pattern compatibility with artificially fractured wells, improve the waterflooding effect in low-permeability reservoirs by using large well spacing, small row spacing, and rhomboid inverted nine-point or five-point rectangular water injection well patterns. However, in the long-term water injection development process, the low permeability of the matrix, natural fractures, and the high conductivity of various artificial fractures can lead to premature or rapid opening and extension of various fractures in the reservoir, resulting in widespread water-induced fractures. The opening of water-induced fractures can cause sudden water flooding of oil wells, reducing the waterflooded volume. Therefore, water-induced fractures are a key factor determining the effectiveness of waterflooding in low-permeability reservoirs and the distribution of remaining oil. Predicting, warning, and preventing water-induced fractures is of significant guiding importance for water injection development in low-permeability reservoirs.

[0003] The Chinese patent "A Method for Predicting and Evaluating Water Injection-Induced Fractures in Low-Permeability Reservoirs" (Application Date: 2016.05.04; Application No.: CN2016102890030; Publication Date: 2016.09.21; Publication No.: CN105952427A) discloses a method for identifying single-well induced fractures; determining the formation mechanism and main controlling factors of water injection-induced fractures; predicting water injection-induced fractures based on the identification of single-well induced fractures and the determined formation mechanism and main controlling factors; and finally evaluating the prediction results. However, the prediction assumes that the induced fractures only open along the direction of the maximum horizontal principal stress. In reality, many reservoirs have induced fractures along the direction connecting multiple injection and production wells, resulting in significant discrepancies with the predicted results. This leads to inaccurate predictions, causing multi-directional water flooding of wells and poor reliability. Summary of the Invention

[0004] The purpose of this invention is to provide an early warning method for water injection-induced fractures based on an area-based water injection well network, which solves the problems of inaccurate and unreliable prediction results of existing water injection-induced fractures.

[0005] The technical solution adopted in this invention is a method for early warning of water injection-induced fractures based on an area-based water injection well network, comprising the following steps:

[0006] Step 1: Obtain reservoir geostress characteristic parameters, rock mechanics parameters, reservoir development characteristic parameters, and reservoir injection and production parameters;

[0007] Step 2: For the injection-production well group, an area water injection well network is deployed, and the critical pressure for water injection-induced fracture opening in each injection-production line direction within the well group is calculated.

[0008] Step 3: Select the minimum critical water injection pressure in each direction of the injection-production line in Step 2 as the early warning water injection pressure, and the corresponding direction as the early warning direction;

[0009] Step 4: Calculate the critical water injection intensity for single-well water injection to induce fracture opening, and use it as the early warning water injection intensity;

[0010] Step 5: Combine the early warning water injection pressure and direction obtained in Step 3 with the early warning water injection intensity obtained in Step 4 to conduct single-well water injection induced fracture early warning.

[0011] The invention is further characterized in that:

[0012] Step 1 involves obtaining reservoir geostress characteristic parameters, rock mechanics parameters, reservoir development characteristic parameters, and reservoir injection and production parameters.

[0013] The reservoir stress characteristic parameters include the maximum and minimum principal stresses of the current stress field;

[0014] Rock mechanical parameters include overlying strata pressure, uniaxial compressive strength of rock, Poisson's ratio of rock, and tensile strength of rock;

[0015] Reservoir development characteristic parameters include the burial depth of natural fractures, the dip angle of natural fractures, and formation pore pressure;

[0016] Reservoir injection and production parameters include daily water injection volume per well and bottom hole pressure of injection wells.

[0017] The conditions for the formation of water-injection induced fractures in step 2 include three formation mechanisms. The critical pressure for the opening of water-injection induced fractures in each injection-production line direction within the well group under each of the three formation mechanisms is calculated.

[0018] Mechanism 1: When the water injection pressure exceeds the opening pressure of a natural fracture, the natural fracture opens, expands, and extends, forming a water-induced fracture. The critical pressure for the opening of a water-induced fracture is equal to the opening pressure of a natural fracture. The natural fracture opening pressure is calculated as follows:

[0019]

[0020] In the formula, P i P is the pressure at which a natural fracture opens, expressed in MPa; μ is the Poisson's ratio of the rock; P o P represents the pressure of the overlying strata, expressed in MPa. p σ represents the formation pore pressure, in MPa; H represents the depth of the natural fracture, in m; H σ1 is the maximum principal stress of the current stress field, in MPa; θ is the dip angle of the natural fracture; β is the angle between the current geostress direction and the fracture direction, in °; σ1 is the current horizontal geostress, in MPa.

[0021] The current horizontal ground stress is calculated as follows:

[0022] σ1=σ h +(σ H -σ h Sinα (2)

[0023] In the formula, σ1 is the current horizontal ground stress, with units of MPa; σ h α represents the minimum principal stress in the current stress field, in MPa; α is the angle between the line connecting the injection and production wells and the direction of the natural fracture, in °.

[0024] Mechanism 2: Hydraulic fractures formed when the injection pressure exceeds the formation fracturing pressure. The calculated fracturing pressure is:

[0025] P f =3σ h -σ H +σ t -P p (3)

[0026] In the formula, P f Pp is the formation fracture pressure, in MPa; σ is the formation pore pressure, in MPa; H σ represents the maximum principal stress in the current stress field, measured in MPa. h σ represents the minimum principal stress in the current stress field, expressed in MPa. t The tensile strength of rock is expressed in MPa.

[0027] The tensile strength of the rock is calculated as follows:

[0028] σ t =σ c / K (4)

[0029] In the formula, K is a constant with a value of 12.26; σ c This represents the uniaxial compressive strength of rock, expressed in MPa.

[0030] The uniaxial compressive strength of the rock is calculated as follows:

[0031] σ c =(0.0045+0.0035V) cl )·E (5)

[0032] In the formula, σ c V represents the uniaxial compressive strength of rock, expressed in MPa. cl is the clay content, %; E is the dynamic Young's modulus of the layer, in GPa;

[0033] Calculate the clay content:

[0034]

[0035] In the formula, G cur The Hilvhie index is related to geological age;

[0036] Calculate the reservoir gamma coefficient:

[0037] I r =(rr min ) / (r max -r min (7)

[0038] In the formula, I r r is the reservoir gamma coefficient; r is the reservoir gamma value; r max The gamma value of pure mudstone in the reservoir; r min The gamma value is for pure sandstone reservoir.

[0039] Mechanism 3: When the water injection pressure exceeds the artificial fracture opening pressure or fracture extension pressure, the artificial fracture opens or extends, inducing a fracture. Calculate the artificial fracture closing pressure:

[0040]

[0041] In the formula, P e σ is the closure pressure of the crack, measured in MPa; h P is the minimum principal stress of the current stress field, in MPa; μ is the Poisson's ratio of the rock; P0 is the formation pressure, in MPa; P p This represents the formation pore pressure, expressed in MPa.

[0042] Calculate the artificial crack propagation pressure:

[0043]

[0044] In the formula, P fe The crack propagation pressure is expressed in MPa; E is Young's modulus, expressed in MPa; and G is the crack surface energy, expressed in J / cm². 3 ;

[0045] The half-seam length is calculated as follows:

[0046]

[0047] In the formula, L f V is half the seam length, in meters. p The volume of the proppant is in cubic meters (m³). 3 h represents the oil layer thickness, in meters; P 净 The pressure in the well is measured in MPa.

[0048] In step 4, the critical water injection intensity is calculated as follows:

[0049]

[0050] In the formula, h is the depth of the crack burial, in meters; Q w This represents the daily water injection volume per well, in cubic meters (m³). 3 / d; Critical water injection intensity, in meters (m). 3 / d·m; k is the permeability, in units of 10. -3 μm 2 ,P H This refers to the bottom pressure of the injection well, expressed in MPa. Mean formation pressure, in MPa; G is the initiation pressure gradient, in MPa / m; B w R is the volume coefficient of water; e The supply radius is in meters (m); r w The radius of the injection well is in meters (m).

[0051] The beneficial effects of this invention are as follows: The method of this invention simultaneously considers the early warning water injection pressure, early warning direction, and early warning water injection intensity through the area water injection well network. Based on these parameters, it can quickly predict water injection-induced fractures in low-permeability reservoirs. The obtained prediction results are more accurate and consistent with reality, which helps to predict, warn, and prevent water injection-induced fractures in area water injection development reservoirs. This helps to control the water drive development effect and the distribution law of remaining oil in low-permeability reservoirs, effectively guide the development of low-permeability reservoirs, maintain the safety and stability of oil wells, and provide solid support for the safety assurance of oil wells. Attached Figure Description

[0052] Figure 1 This is a flowchart of the water injection-induced fracture early warning method based on area water injection well network of the present invention;

[0053] Figure 2 This is a graph showing the current horizontal stress variation in Embodiment 3 of the present invention.

[0054] Figure 3 The critical water injection pressure for inducing fracture opening by water injection in different injection-production connection directions within a well network of a certain well group in an oil reservoir, as described in Example 4 of this invention. Detailed Implementation

[0055] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0056] Example 1

[0057] This invention provides a method for early warning of water injection-induced fractures based on an area-based water injection well network, the flowchart of which is shown below. Figure 1 As shown, it includes the following steps:

[0058] Step 1: Obtain reservoir geostress characteristic parameters, rock mechanics parameters, reservoir development characteristic parameters, and reservoir injection and production parameters;

[0059] Step 2: For the injection-production well group, an area water injection well network is deployed, and the critical pressure for water injection-induced fracture opening in each injection-production line direction within the well group is calculated.

[0060] Step 3: Select the minimum critical water injection pressure in each direction of the injection-production line in Step 2 as the early warning water injection pressure, and the corresponding direction as the early warning direction;

[0061] Step 4: Calculate the critical water injection intensity for single-well water injection to induce fracture opening, and use it as the early warning water injection intensity;

[0062] Step 5: Combine the early warning water injection pressure and direction obtained in Step 3 with the early warning water injection intensity obtained in Step 4 to conduct single-well water injection induced fracture early warning.

[0063] This invention provides a method for early warning of water-induced fractures based on an area-based water injection well network. The method employs an area-based water injection well network for deployment. By calculating the critical pressure for initiating water-induced fractures along the direction connecting each injection and production well, the minimum value is selected as the early warning water injection pressure, and the corresponding direction is used as the early warning direction. Combined with the calculation of the critical water injection intensity for initiating water-induced fractures in a single well, the method obtains prediction results quickly, accurately, and quantitatively, greatly improving prediction accuracy. This provides strong technical support for the design of water injection development schemes for low-permeability oil reservoirs, maintaining the normal operation and safety protection of oil wells.

[0064] Example 2

[0065] This invention provides a method for early warning of water injection-induced fractures based on an area-based water injection well network, comprising the following steps:

[0066] Step 1: Obtain reservoir geostress characteristic parameters, rock mechanics parameters, reservoir development characteristic parameters, and reservoir injection and production parameters;

[0067] The reservoir stress characteristic parameters include the maximum and minimum principal stresses of the current stress field;

[0068] Rock mechanical parameters include overlying strata pressure, uniaxial compressive strength of rock, formation pore pressure, Poisson's ratio of rock, and tensile strength of rock;

[0069] Reservoir development characteristic parameters include the depth of natural fractures and the dip angle of natural fractures;

[0070] Reservoir injection and production parameters include daily water injection volume per well and bottom hole pressure of injection wells.

[0071] Step 2: For the injection-production well group, an area water injection well network is deployed, and the critical pressure for water injection-induced fracture opening in each injection-production line direction within the well group is calculated.

[0072] Step 2 specifically involves calculating the critical pressure for the formation of water-induced fractures under three formation mechanisms, and calculating the critical pressure for the opening of water-induced fractures in each injection-production line direction within the well group under each of the three formation mechanisms.

[0073] Step 4: Calculate the critical water injection intensity for single-well water injection to induce fracture opening, and use it as the early warning water injection intensity;

[0074] Step 5: Combine the early warning water injection pressure and direction obtained in Step 3 with the early warning water injection intensity obtained in Step 4 to conduct single-well water injection induced fracture early warning.

[0075] Example 3

[0076] This invention provides a method for early warning of water injection-induced fractures based on an area-based water injection well network, comprising the following steps:

[0077] Step 1: Obtain reservoir geostress characteristic parameters, rock mechanics parameters, reservoir development characteristic parameters, and reservoir injection and production parameters;

[0078] The reservoir stress characteristic parameters include the maximum and minimum principal stresses of the current stress field;

[0079] Rock mechanical parameters include overlying strata pressure, uniaxial compressive strength of rock, formation pore pressure, Poisson's ratio of rock, and tensile strength of rock;

[0080] Reservoir development characteristic parameters include the depth of natural fractures and the dip angle of natural fractures;

[0081] Reservoir injection and production parameters include daily water injection volume per well and bottom hole pressure of injection wells.

[0082] Step 2: For the injection-production well group, an area water injection well network is deployed, and the critical pressure for water injection-induced fracture opening in each injection-production line direction within the well group is calculated.

[0083] Step 2 specifically involves calculating the critical pressure for the formation of water-induced fractures under three formation mechanisms, and calculating the critical pressure for the opening of water-induced fractures in each injection-production line direction within the well group under each of the three formation mechanisms.

[0084] Mechanism 1: When the water injection pressure exceeds the opening pressure of a natural fracture, the natural fracture opens, expands, and extends, forming a water-induced fracture. The critical pressure for the opening of a water-induced fracture is equal to the opening pressure of a natural fracture. The natural fracture opening pressure is calculated as follows:

[0085]

[0086] In the formula, P i P is the pressure at which a natural fracture opens, expressed in MPa; μ is the Poisson's ratio of the rock; P o P represents the pressure of the overlying strata, expressed in MPa.p σ represents the formation pore pressure, in MPa; H represents the depth of the natural fracture, in m; H σ1 is the maximum principal stress of the current stress field, in MPa; θ is the dip angle of the natural fracture; β is the angle between the current geostress direction and the fracture direction, in °; σ1 is the current horizontal geostress, in MPa.

[0087] The current horizontal ground stress is calculated as follows:

[0088] σ1=σ h +(σ H -σ h Sinα (2)

[0089] In the formula, σ1 is the current horizontal ground stress, with units of MPa; σ h The minimum principal stress of the current stress field is given in MPa; α is the angle between the line connecting the injection and production wells and the natural fracture strike, in degrees; the current horizontal geostress variation curve is shown below. Figure 2 As shown.

[0090] Mechanism 2: Hydraulic fractures formed when the injection pressure exceeds the formation fracturing pressure. The calculated fracturing pressure is:

[0091] P f =3σ h -σ H +σ t -P p (3)

[0092] In the formula, P f Pp is the formation fracture pressure, in MPa; σ is the formation pore pressure, in MPa; H σ represents the maximum principal stress in the current stress field, measured in MPa. h σ represents the minimum principal stress in the current stress field, expressed in MPa. t The tensile strength of rock is expressed in MPa.

[0093] The tensile strength of the rock is calculated as follows:

[0094] σ t =σ c / K (4)

[0095] In the formula, K is a constant with a value of 12.26; σ c This represents the uniaxial compressive strength of rock, expressed in MPa.

[0096] The uniaxial compressive strength of the rock is calculated as follows:

[0097] σ c =(0.0045+0.0035V) cl )·E (5)

[0098] In the formula, σ c V represents the uniaxial compressive strength of rock, expressed in MPa. cl is the clay content, %; E is the dynamic Young's modulus of the layer, in GPa;

[0099] Calculate the clay content:

[0100]

[0101] In the formula, G cur The Hilvhie index is related to geological age;

[0102] Calculate the reservoir gamma coefficient:

[0103] I r =(rr min ) / (r max -r min (7)

[0104] In the formula, I r r is the reservoir gamma coefficient; r is the reservoir gamma value; r max The gamma value of pure mudstone in the reservoir; r min The gamma value is for pure sandstone reservoir.

[0105] Mechanism 3: When the water injection pressure exceeds the artificial fracture opening pressure or fracture extension pressure, the artificial fracture opens or extends, inducing a fracture. Calculate the artificial fracture closing pressure:

[0106]

[0107] In the formula, P e σ is the closure pressure of the crack, measured in MPa; h P is the minimum principal stress of the current stress field, in MPa; μ is the Poisson's ratio of the rock; P0 is the formation pressure, in MPa; P p This represents the formation pore pressure, expressed in MPa.

[0108] Calculate the artificial crack propagation pressure:

[0109]

[0110] In the formula, P fe The crack propagation pressure is expressed in MPa; E is Young's modulus, expressed in MPa; and G is the crack surface energy, expressed in J / cm². 3 ;

[0111] The half-seam length is calculated as follows:

[0112]

[0113] In the formula, L f V is half the seam length, in meters. p The volume of the proppant is in cubic meters (m³). 3 h represents the oil layer thickness, in meters; P 净 The pressure in the well is measured in MPa.

[0114] Step 3: Select the minimum critical water injection pressure in each direction of the injection-production line in Step 2 as the early warning water injection pressure. This direction is the early warning direction.

[0115] Step 4: Calculate the critical water injection intensity for single-well water injection to induce fracture opening, and use it as the early warning water injection intensity;

[0116] The critical water injection intensity is calculated as follows:

[0117]

[0118] In the formula, h is the depth of the crack burial, in meters; Q w This represents the daily water injection volume per well, in cubic meters (m³). 3 / d; Critical water injection intensity, in meters (m). 3 / d·m; k is the permeability, in units of 10. -3 μm 2 ,P H ρ is the bottom hole pressure of the injection well, in MPa; p is the average formation pressure, in MPa; G is the starting pressure gradient, in MPa / m; B w R is the volume coefficient of water; e The supply radius is in meters (m); r w The radius of the injection well is in meters (m).

[0119] Step 5: Combine the early warning water injection pressure and direction obtained in Step 3 with the early warning water injection intensity obtained in Step 4 to conduct single-well water injection induced fracture early warning.

[0120] Example 4

[0121] This invention relates to a method for early warning of water injection-induced fractures based on an area-based water injection well network, comprising the following steps:

[0122] Step 1: Obtain reservoir geostress characteristic parameters, rock mechanics parameters, reservoir development characteristic parameters, and reservoir injection and production parameters;

[0123] Step 2: For the injection-production well group, an area water injection well network is deployed, and the critical pressure for water injection-induced fracture opening in each injection-production line direction within the well group is calculated.

[0124] Step 3: Select the minimum critical injection pressure in each direction of the injection-production line from Step 2 as the early warning injection pressure, and the corresponding direction as the early warning direction; for example... Figure 3 As shown, the early warning pressure for the water injection-induced fracture opening in this well group is 48.2 MPa, and the early warning direction for the water injection-induced fracture opening is 70° northeast, followed by the near east-west and near north-south injection-production line directions.

[0125] Step 4: Calculate the critical injection intensity for fracture initiation induced by water injection in a single well, as the early warning injection intensity; the calculated critical injection intensity for this well group is 2.98m. 3 / d·m.

[0126] Step 5: Input the warning water injection pressure obtained in Step 3 and the warning water injection intensity obtained in Step 4 into the warning device to perform single-well water injection induced fracture warning.

[0127] This invention presents a method for early warning of water-induced fractures based on area-based water injection well networks. It calculates the critical pressure for the initiation of water-induced fractures in each direction of the injection-production line within the well group, and uses the minimum critical water injection pressure in each direction as the early warning water injection pressure. It also calculates the critical water injection intensity for the initiation of water-induced fractures in a single well as the early warning water injection intensity. This method has significant advantages in improving detection accuracy, coverage, and real-time performance. It helps to predict, warn, and prevent water-induced fractures in reservoirs developed through area-based water injection, thereby controlling the water-drive development effect and residual oil distribution in low-permeability reservoirs, effectively guiding the development of low-permeability reservoirs, and is of great significance for the safety protection of oil wells.

Claims

1. A method for early warning of water injection-induced fractures based on area-based water injection well networks, characterized in that, Includes the following steps: Step 1: Obtain reservoir geostress characteristic parameters, rock mechanics parameters, reservoir development characteristic parameters, and reservoir injection and production parameters; Step 2: For the injection-production well group, an area water injection well network is deployed, and the critical pressure for water injection-induced fracture opening in each injection-production line direction within the well group is calculated. Step 3: Select the minimum critical water injection pressure in each direction of the injection-production line in Step 2 as the early warning water injection pressure, and the corresponding direction as the early warning direction; Step 4: Calculate the critical water injection intensity for single-well water injection to induce fracture opening, and use it as the early warning water injection intensity; Step 5: Combine the early warning water injection pressure and direction obtained in Step 3 with the early warning water injection intensity obtained in Step 4 to conduct single-well water injection induced fracture early warning.

2. The method for early warning of water injection-induced fractures based on area-based water injection well networks according to claim 1, characterized in that, Step 1 involves obtaining reservoir geostress characteristic parameters, rock mechanics parameters, reservoir development characteristic parameters, and reservoir injection and production parameters. The reservoir stress characteristic parameters include the maximum and minimum principal stresses of the current stress field; Rock mechanical parameters include overlying strata pressure, uniaxial compressive strength of rock, formation pore pressure, Poisson's ratio of rock, and tensile strength of rock; Reservoir development characteristic parameters include the depth of natural fractures and the dip angle of natural fractures; Oil reservoir injection and production parameters include injection well pressure and daily water injection volume per well.

3. The method for early warning of water injection-induced fractures based on area-based water injection well networks according to claim 2, characterized in that, The conditions for the formation of water-injection induced fractures in step 2 include three formation mechanisms. The critical pressure for the opening of water-injection induced fractures in each injection-production line direction within the well group under each of the three formation mechanisms is calculated.

4. The method for early warning of water injection-induced fractures based on area-based water injection well networks according to claim 3, characterized in that, In step 2, mechanism one: the water injection pressure exceeds the opening pressure of the natural fracture, causing the natural fracture to open, expand, and extend, forming a water-induced fracture. The critical pressure for the opening of the water-induced fracture is the opening pressure of the natural fracture. The natural fracture opening pressure is calculated as follows: In the formula, P i P is the pressure at which a natural fracture opens, expressed in MPa; μ is the Poisson's ratio of the rock; P o P represents the pressure of the overlying strata, expressed in MPa. p σ represents the formation pore pressure, in MPa; H represents the depth of the natural fracture, in m; H σ1 is the maximum principal stress of the current stress field, in MPa; θ is the dip angle of the natural fracture; β is the angle between the current geostress direction and the fracture direction, in °; σ1 is the current horizontal geostress, in MPa. The current horizontal ground stress is calculated as follows: σ1=σ h +(s H -s h )Sina (2) In the formula, σ1 is the current horizontal ground stress, with units of MPa; σ h α represents the minimum principal stress of the current stress field, in MPa; α is the angle between the line connecting the injection and production wells and the direction of the natural fracture, in °.

5. The method for early warning of water injection-induced fractures based on area-based water injection well networks according to claim 4, characterized in that, In step 2, mechanism two: hydraulic fractures formed when the injection pressure exceeds the formation fracturing pressure. The fracturing pressure is calculated as follows: P f =3σ h -s H +s t -P p (3) In the formula, P f Pp is the formation fracture pressure, in MPa; σ is the formation pore pressure, in MPa; H σ represents the maximum principal stress in the current stress field, measured in MPa. h σ represents the minimum principal stress in the current stress field, expressed in MPa. t The tensile strength of rock is expressed in MPa. The tensile strength of the rock is calculated as follows: s t =s c / K (4) In the formula, K is a constant with a value of 12.26; σ c This represents the uniaxial compressive strength of rock, expressed in MPa. The uniaxial compressive strength of the rock is calculated as follows: s c =(0.0045+0.0035V cl )·E (5) In the formula, σ c V represents the uniaxial compressive strength of rock, expressed in MPa. cl is the clay content, %; E is the dynamic Young's modulus of the layer, in GPa; Calculate the clay content: In the formula, G cur The Hilvhie index is related to geological age; Calculate the reservoir gamma coefficient: I r ＝(r-r min ) / (r max -r min ) (7) In the formula, I r r is the reservoir gamma coefficient; r is the reservoir gamma value; r max The gamma value of pure mudstone in the reservoir; r min The gamma value is for pure sandstone reservoir.

6. The method for early warning of water injection-induced fractures based on area-based water injection well networks according to claim 5, characterized in that, In step 2, mechanism 3: the water injection pressure is higher than the artificial fracture opening pressure or fracture extension pressure, causing the artificial fracture to open or extend, thus inducing a fracture. The artificial fracture closing pressure is then calculated. In the formula, P e σ is the closure pressure of the crack, measured in MPa; h P is the minimum principal stress of the current stress field, in MPa; μ is the Poisson's ratio of the rock; P0 is the formation pressure, in MPa; P p This represents the formation pore pressure, expressed in MPa. Calculate the artificial crack propagation pressure: In the formula, P fe The crack propagation pressure is expressed in MPa; E is Young's modulus, expressed in MPa; and G is the crack surface energy, expressed in J / cm². 3 ; The half-seam length is calculated as follows: In the formula, L f V is half the seam length, in meters. p The volume of the proppant is in cubic meters (m³). 3 h represents the oil layer thickness, in meters; P 净 The pressure in the well is measured in MPa.

7. The method for early warning of water injection-induced fractures based on area-based water injection well networks according to claim 6, characterized in that, In step 4, the critical water injection intensity is calculated as follows: In the formula, h is the depth of the crack burial, in meters; Q w This represents the daily water injection volume per well, in cubic meters (m³). 3 / d; Critical water injection intensity, in meters (m). 3 / d·m; k is the permeability, in units of 10. -3 μm 2 ,P H This refers to the bottom pressure of the injection well, expressed in MPa. Mean formation pressure, in MPa; G is the initiation pressure gradient, in MPa / m; B w R is the volume coefficient of water; e The supply radius is in meters (m); r w The radius of the injection well is in meters (m).

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